I am currently reading "The Alexiad of Anna Comnena" and she refers to a Frenchman named Bohemond as being unable to "out-Cretan a Cretan" in reference to Bohemond's dealings with the Byzantine Emperor Alexius. I think I have a basic understanding of what Anna (writing in the 12th century) is saying here, but if someone with more historical might than myself could give an explanation I would appreciate it. Cheers!
'To out-Herod Herod' is to be a wicked person who commits atrocities. In the middle ages Herod the Great of Judea was the archetype of an evil, cruel and bloodstained ruler, in much the same way as Hitler is today. He gained this reputation particularly in reference to the Bible story of the Massacre of the Innocents in which the children of Bethlehem were murdered at his command.